In recent years, in addition to a semiconductor element which controls the flow of electrons, spintronics (which may be referred to as spinelectronics, magnetoelectronics or spinics) for controlling the spin as a source of magnetism by the semiconductive method has been developing. With the development of such spintronics, a practical application of a MRAM (Magnetic Random Access Memory), a novel light emitting element, etc., has been expected.
The MRAM which stores data magnetically is expected as a next generation memory, as the MRAM has such beneficial characteristics as nonvolatile, high data writing speed, which is difficult to be realized by the conventional semiconductor memory (DRAM, SRAM, EEPROM).
FIG. 15(a) and FIG. 15(b) are conceptual diagrams illustrating the structure of a conventional MRAM. In this MRAM, a tunneling magnetoresistive (TMR: Tunneling Magnetoresistance) element is adopted. A TMR element 50 includes a very thin layer (insulative layer 53) of insulative substance of only a few atoms thick, which is interposed between two magnetic layers (a first magnetic layer 51 and a second magnetic layer 52). In this TMR element 50, electric resistance changes according to magnetization directions of the first magnetic layer and the second magnetic layers 51 and 52.
For example, when current is applied to the TMR element 50 in the direction shown in FIG. 15(a), in an electric wire 54 on the side of the TMR element 50, a magnetic field is generated to the right in FIG. 15(a), and is magnetized in the direction of the magnetic field generated by the first magnetic layer 51 of the TMR element 50. Incidentally, the magnetization direction of the second magnetic layer 52 is set to the right in FIG. 15(a), and not to be changed by the current flowing in the electric wire 54. In this state, current becomes more smoothly flow in the thin insulative layer 53 by the tunneling effect, and the resistance value of the TMR element 50 is lowered accordingly.
On the other hand, when current is applied to the TMR element 50 in the direction shown in FIG. 15(b), in the electric wire 54 on the side of the TMR element 50, a magnetic field is generated to the left in FIG. 15(b), and is magnetized in the direction of the magnetic field generated by the first magnetic layer 51 of the TMR element 50. In this state, current becomes difficult to flow in the thin insulative layer 53, and the resistance value of the TMR element 50 is increased accordingly.
By utilizing the foregoing changes in resistance (TMR effect), data can be stored in the TMR element 50, for example, by setting the state of FIG. 15(a) as “0”, and the state of FIG. 15(b) as “1”.
On the other hand, for a novel light emitting element, the development of such element that can control the polarization state of light as desired has been expected. For example, for the observation of the spinning state of the substance, a circularly polarized light is adopted. Conventionally, this circularly polarized light is obtained, for example, as a radiation from a circular accelerator of the synchrotron-type, or by making a linearly polarized light pass through a predetermined filter. However, such circular accelerator has a large scale structure, and the device which makes the light pass through the filter also has a relatively complicated structure. It is therefore preferable to obtain a circularly polarized light by means of a single element. The generation of such circularly polarized light is reported, for example, in the Nature vol. 402 16 Dec. 1999 pp. 790-792.
FIG. 16 is a cross-sectional view illustrating the structure of the element article. This element is arranged so as to include an n-type GaAs substrate 61, an n-type GaAs buffer 62, GaAs 63, an (In, Ga)As quantum well 64, a GaAs spacer 65 and a p-type GaMnAs 66 which are laminated in this order. With respect to this element, by applying the magnetic field B parallel to the magnetization easy axis of the p-type GaMnAs 66 to apply current I, the spin polarized positive hole h+reaches the (In, Ga) As quantum well 64 via the non-magnetic GaAs spacer 65, and is reconnected to the electron which is not spin polarized at the (In, Ga) As quantum well 64, and the element emits a circularly polarized lights σ+ as being reconnected to the electrons of the non-spin polarized electrons.
However, the foregoing conventional technique has the following problems.
Firstly, with regard to MRAM shown in FIG. 15(a) and FIG. 15(b), it is required to form an exteremely thin insulative layer 53 in the TMR element 50 to obtain an appropriate TMR effect. For this reason, the conditions for forming the TMR element 50 become very strict, which hinder the practical applications.
For the element shown in FIG. 16, as the light emitted therefrom has a low degree of polarization, and it is not possible to be uses as a light emitting element which emits a circularly polarized light. Incidentally, the foregoing article does not aim to generate a circularly polarized light. In this element of FIG. 16, it is necessary to arrange so as to generate a circularly polarized light at low temperatures, i.e., at 50 K or below.
The present invention is achieved in finding a solution to the foregoing problem, and the first object of the present invention is to provide an element which offers an appropriate TMR effects. It is an second object of the present invention to provide an element which emits a circularly polarized light with a high degree of polarization.